Allowing specific source to specific uri and deny rest all

Normally you do this based in the path, because is likely the application will have multiple pages:

when HTTP_REQUEST {
if [class match [IP::client_addr] equals "DG1"] {
    if { not ([HTTP::path] starts_with "/services/user1/"]) } {
        HTTP::redirect "https://www.testdev.com/services/user1/"
        return
    }
    drop
}

If you really want the URI:

when HTTP_REQUEST {
if [class match [IP::client_addr] equals "DG1"] {
    if { not ([HTTP::uri] starts_with "/services/user1.html"]) } {
        HTTP::redirect "https://www.testdev.com/services/user1.html"
        return
    }
    drop
}